U.S. patent application number 15/673147 was filed with the patent office on 2019-02-14 for calcite channel nanofluidics.
The applicant listed for this patent is Saudi Arabian Oil Company. Invention is credited to Mohammed Al Otaibi, Ali Abdallah Al-Yousef, Dong Kyu Cha.
Application Number | 20190049847 15/673147 |
Document ID | / |
Family ID | 63405414 |
Filed Date | 2019-02-14 |
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United States Patent
Application |
20190049847 |
Kind Code |
A1 |
Cha; Dong Kyu ; et
al. |
February 14, 2019 |
CALCITE CHANNEL NANOFLUIDICS
Abstract
A method for fabricating calcite channels in a nanofluidic
device is described. A photoresist is coated on a substrate, and a
portion of the photoresist is then exposed to a beam of electrons
in a channel pattern. The exposed portion of the photoresist is
developed to form a channel pattern, and calcite is deposited in
the channel pattern using a calcite precursor gas. The deposited
calcite includes at least one side having a length in a range of
approximately 50 to 100 nanometers. The photoresist remaining after
developing the exposed portion of the photoresist is removed.
Inventors: |
Cha; Dong Kyu; (Abqaiq,
SA) ; Al Otaibi; Mohammed; (Abqaiq, SA) ;
Al-Yousef; Ali Abdallah; (Dhahran, SA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saudi Arabian Oil Company |
Dhahran |
|
SA |
|
|
Family ID: |
63405414 |
Appl. No.: |
15/673147 |
Filed: |
August 9, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/325 20130101;
G03F 7/40 20130101; G03F 7/038 20130101; G03F 7/0757 20130101; G03F
7/2059 20130101 |
International
Class: |
G03F 7/20 20060101
G03F007/20 |
Claims
1. A method of fabricating calcite channels in a nanofluidic
device, the method comprising: coating a photoresist on a
substrate; exposing a portion of the photoresist to a beam of
electrons, wherein the portion is exposed in a channel pattern;
developing the exposed portion of the photoresist to form the
channel pattern; depositing calcite in the channel pattern using a
calcite precursor gas, wherein the deposited calcite has a width in
a range of approximately 50 to 100 nanometers; and removing the
photoresist remaining after developing the exposed portion of the
photoresist.
2. The method of claim 1, wherein the substrate comprises
silicon.
3. The method of claim 1, wherein the photoresist comprises a
negative photoresist.
4. The method of claim 3, wherein the negative photoresist
comprises polydimethylsiloxane (PDMS) or SU-8.
5. The method of claim 1, wherein developing the photoresist
comprises dissolving the photoresist using a solvent and revealing
a portion of the substrate.
6. The method of claim 5, wherein the solvent comprises propylene
glycol methyl ether acetate (PGMEA), ethyl lactate, or di-acetone
alcohol.
7. The method of claim 1, further comprising packaging the device
in a casing, wherein the casing comprises: a top portion comprising
a window; a bottom portion configured to hold the device; an inlet
connection configured to allow a fluid to enter the device; and an
outlet connection configured to allow the fluid to exit the
device.
8. The method of claim 7, wherein the window comprises an
electrically conductive and optically transparent material.
9. The method of claim 8, wherein the conductive and transparent
material comprises silicon nitride (SiN).
10. A system comprising: a nanofluidic device, wherein the device
comprises a bottom portion comprising a substrate and a top portion
comprising a calcite channel structure, the calcite channel
structure comprising a width in a range of approximately 50 to 100
nanometers; a casing for the device; and an electron source for
providing a beam of electrons.
11. The system of claim 10, wherein the substrate comprises
silicon.
12. The system of claim 10, wherein the electron source is a
scanning electron microscope (SEM).
13. The system of claim 10, wherein the casing comprises: a top
portion comprising a window; a bottom portion configured to hold
the device; an inlet connection configured to allow a fluid to
enter the device; and an outlet connection configured to allow the
fluid to exit the device.
14. The system of claim 13, wherein the window comprises an
electrically conductive and optically transparent material.
15. The system of claim 14, where in the conductive and transparent
material comprises silicon nitride (SiN).
Description
TECHNICAL FIELD
[0001] This specification relates to nanofluidics and more
specifically for petrophysical application.
BACKGROUND
[0002] Enhanced oil recovery methods are utilized to increase the
amount of crude oil that can be extracted from an oil field. At
small scales (channel sizes on the order or nanometers or
micrometers), fluids can behave differently in that factors such as
surface tension begin to dominate the system. With better
understanding of fluid behavior at small scales, enhanced oil
recovery methods can be improved to extract even more oil from a
source rock or reservoir. Microfluidic models which can replicate
conditions found in underground reservoirs have been developed to
observe, evaluate, and understand physical and chemical phenomena
in oil extraction and recovery.
SUMMARY
[0003] The present disclosure describes a method of fabricating
calcite channels for nanofluidics. Certain aspects of the subject
matter described here can be implemented as a method. Calcite
channels are fabricated in a nanofluidic device. A photoresist is
coated on a substrate, and a portion of the photoresist is exposed
to a beam of electrons in a channel pattern. The exposed portion of
the photoresist is developed to form a channel pattern, and calcite
is deposited in the channel pattern using a calcite precursor gas.
The deposited calcite includes at least one side having a length in
a range of approximately 50 to 100 nanometers (nm). The photoresist
remaining after developing the exposed portion of the photoresist
is removed.
[0004] This, and other aspects, can include one or more of the
following features. The substrate can be silicon. The photoresist
can be a negative photoresist, such as polydimethylsiloxane (PDMS)
or SU-8. Developing the photoresist can include dissolving the
photoresist using a solvent and revealing a portion of the
substrate. The solvent used to dissolve the photoresist can be
propylene glycol methyl ether acetate (PGMEA), ethyl lactate, or
di-acetone alcohol. Fabricating calcite channels in the nanofluidic
device can include packaging the device in a casing. The casing can
include a top portion which includes a window, a bottom portion to
hold the device, an inlet connection to allow a fluid to enter the
device, and an outlet connection to allow the fluid to exit the
device. The window can be an electrically conductive and optically
transparent material, such as silicon nitride (SiN).
[0005] Certain aspects of the subject matter described here can be
implemented as a system. The system includes a nanofluidic device,
a casing for the device, and an electron source for providing a
beam of electrons. The device includes a bottom portion which
includes a substrate, and a top portion which includes a calcite
channel structure. The calcite channel structure includes at least
one side having a length in a range of approximately 50 to 100 nm.
This, and other aspects, can include one or more of the following
features. The substrate can be silicon. The electron source can be
a scanning electron microscope (SEM). The casing can include a top
portion which includes a window, a bottom portion to hold the
device, an inlet connection to allow a fluid to enter the device,
and an outlet connection to allow the fluid to exit the device. The
window can be an electrically conductive and optically transparent
material, such as SiN.
[0006] The details of one or more implementations of the subject
matter of this specification are set forth in the accompanying
drawings and the description. Other features, aspects, and
advantages of the subject matter will become apparent from the
description, the drawings, and the claims.
DESCRIPTION OF DRAWINGS
[0007] FIG. 1 is a schematic diagram illustrating an example method
for fabricating a nanofluidic device, according to an
implementation.
[0008] FIG. 2A is a cross-sectional view of a schematic diagram
illustrating an example nanofluidic device, according to an
implementation.
[0009] FIG. 2B is a top view of a schematic diagram illustrating an
example nanofluidic device, according to an implementation.
[0010] FIG. 3 is a schematic diagram illustrating an example
nanofluidic device system, according to an implementation.
[0011] FIG. 4 is a flowchart of an example method for fabricating a
nanofluidic device, according to an implementation.
[0012] Like reference numbers and designations in the various
drawings indicate like elements.
DETAILED DESCRIPTION
[0013] The following detailed description describes a method of
fabricating calcite channels for nanofluidics, and is presented to
enable any person skilled in the art to make and use the disclosed
subject matter in the context of one or more particular
implementations. Various modifications, alterations, and
permutations of the disclosed implementations can be made and will
be readily apparent to those or ordinary skill in the art, and the
general principles defined may be applied to other implementations
and applications, without departing from scope of the disclosure.
In some instances, details unnecessary to obtain an understanding
of the described subject matter may be omitted so as to not obscure
one or more described implementations with unnecessary detail and
inasmuch as such details are within the skill of one of ordinary
skill in the art. The present disclosure is not intended to be
limited to the described or illustrated implementations, but to be
accorded the widest scope consistent with the described principles
and features.
[0014] A portion of the world's oil reserves exists in carbonate
rocks, such as limestone and dolostone. These rocks, however, can
vary considerably in characteristics such as texture, porosity, and
permeability even across areas within the same formation. This
variation makes consistent flow of oil difficult to achieve.
Microfluidics is considered a useful method to characterize crude
oil interactions with different fluids and with rock formations in
petrophysics applications. Conventional calcite (CaCO.sub.3)
channel models comprise etched natural calcite crystal, but these
models are on the scale of micrometers. Fluidics at a nano-scale
(that is, on the order of nanometers), are beneficial to understand
the physical and chemical phenomena of fluid-fluid and
fluid-calcite rock interactions at an atomic scale.
[0015] Referring to FIG. 1, a method 100 for fabricating calcite
channels in a nanofluidic device, starts at 102 by coating a
photoresist on a substrate. In certain implementations, the
photoresist is a negative photoresist, such as polydimethylsiloxane
(PDMS) or SU-8. The substrate can have a clean and flat surface and
can be made of, for example, silicon. The coating of the
photoresist can be performed by spin coating to apply a layer of
photoresist on the substrate at a spin rate in a range of
approximately 500 to 2000 revolutions per minute (rpm). The spin
rate can determine the thickness of the layer of photoresist. The
thickness of the layer of photoresist can determine a height of
resulting calcite channels in the nanofluidic device. Therefore,
the thickness of the photoresist coating can be chosen based on the
desired height for the calcite channels in the nanofluidic device,
for example, a height less than 10 centimeters (cm). The
preparation of photoresist can include edge bead removal (EBR) to
remove any buildup of photoresist on the edge of the substrate. The
preparation of photoresist can include a baking step which involves
baking at approximately 200 degrees Fahrenheit (.degree. F.) for a
duration of time, dependent on the thickness of the layer of
photoresist. The baking temperature can also affect the duration of
the baking step.
[0016] From 102, method 100 proceeds to 104, where a portion of the
photoresist is exposed to a beam of electrons. Exposing a portion
of the photoresist to a beam of electrons can cause the portion of
the photoresist to be removed. In certain implementations, electron
beam lithography, is used to remove the photoresist. Electron beam
lithography is a technique for patterning at nanometer (nm) scale
and includes scanning a beam of electrons on a resist, for example,
PDMS. The lithographic process includes exposure of the resist and
development of the exposed resist to form a pattern in the
remaining resist. Exposure of the resist to an energy source, such
as a beam of electrons, modifies the resist physically, chemically,
or both. In certain implementations, the beam of electrons is
supplied by a scanning electron microscope (SEM). The exposure of
the resist can be followed by a post-exposure baking step which
involves baking at approximately 200.degree. F. for a duration of
time, dependent on the thickness of the layer of photoresist.
[0017] The portion of the photoresist that is exposed to the beam
of electrons can be exposed in a channel pattern. In general, a
portion of the photoresist is exposed to an energy source and
developed to form the channel pattern. Sizes of the channel pattern
can be chosen based on the desired size for the calcite channels in
the nanofluidic device. For positive resists, the development of
the resist removes the exposed portion of the resist. For negative
resists, the development of the resist removes the unexposed
portion of the resist. Developing the resist involves dissolving
the resist using a solvent and revealing a portion of a surface of
the substrate under the photoresist. In certain implementations,
the solvent is an organic solvent, such as propylene glycol methyl
ether acetate (PGMEA), ethyl lactate, or di-acetone alcohol. The
development time depends on the thickness of the layer of
photoresist. The portion of photoresist that remains after
development forms an inverse pattern of the calcite channels in the
finalized nanofluidic device. After development, the device can be
rinsed with fresh solvent, followed by a second wash with another
solvent, such as isopropyl alcohol. The device can then be dried
with a gas, such as nitrogen.
[0018] From 104, method 100 proceeds to 106, where calcite is
deposited in the channel pattern using a calcite precursor gas. In
certain implementations, atomic layer deposition is used to deposit
calcite. Atomic layer deposition is a technique for depositing a
material from a vapor phase and includes a sequence of alternating
introductions of gaseous chemical precursors that react with the
substrate. The individual gas-surface reactions are called
half-reactions. During each half-reaction, a precursor gas is
introduced for a designated amount of time, to allow the precursor
gas to fully react with the substrate surface and deposit a single
layer at the surface. The device is then purged with an inert gas,
such as nitrogen or argon, to remove unreacted precursor, reaction
by-products, or both. The next precursor gas is then introduced to
deposit another layer and similarly purged. The process cycles as
alternating precursor gas is deposited layer by layer until the
desired height is reached. In certain implementations, the atomic
layer deposition process can continue until the calcite layers
reach a similar or same height as the original coating of
photoresist. The deposited calcite can have at least one side with
a length in a range of approximately 50 to 100 nm. From 106, method
100 proceeds to 108, where the photoresist remaining after
developing the exposed portion of the photoresist in 104 is
removed. Removal of the remaining photoresist involves dissolving
the photoresist using a solvent, such as the solvent used in
developing the resist in 104. The remaining calcite and substrate
form the nanofluidic device.
[0019] FIGS. 2A and 2B illustrate a cross-sectional view and a top
view, respectively, of an example nanofluidic device 200. The
device 200 includes a silicon substrate 209 and calcite channels
207. The calcite deposits that make up the channels 207 can have
any shape, such as acylinder or a cuboid. In addition to varying
calcite deposit shapes, the pattern of the calcite channels 207 can
be varied. For example, the channels 207 can have a stacked row
pattern, where the center of each calcite deposit is in line with a
center of a calcite deposit in a row directly above or a row
directly below, as illustrated in FIG. 2B. In some implementations,
the channels 207 can have a shifted row pattern, where the center
of each calcite deposit is not in line with a center of any calcite
deposit in a row directly above or a row directly below. The
straight or curved edges of the calcite deposits and the channel
pattern can represent a variety of geometries that occur in natural
calcite reservoirs. In some implementations, the calcite channels
207 of the nanofluidic device 200 can have a length in a range of
50 to 100 nm in at least one dimension. For example, the width of
each calcite channel 207 can be in the range of 50 to 100 nm.
[0020] Still referring to FIGS. 2A and 2B, the silicon substrate
209 and the calcite channels 207 can be packaged in a casing 211
with a window 201 transparent to an electron beam on top of the
calcite channels 207. In certain implementations, the casing 211
can be made of a conductive metal, and the window 201 can be made
of an electrically conductive material that is also optically
transparent, such as silicon nitride (SiN). Electrical conductivity
allows the window 201 to avoid accumulating an electric charge, and
the transparency of the window 201 allows observation. As
illustrated, the casing has an inlet connection 203 that allows a
fluid, such as brine solution 213, to enter the nanofluidic device
200 and an outlet connection 205 that allows fluid to exit. As
shown in FIGS. 2A, 2B, and 3, the inlet connection 203 and outlet
connection 205 can be located on the same side of device the 200.
In some implementations, the inlet connection 203 and outlet
connection 205 can be located on opposite or adjacent sides of the
device 200.
[0021] FIG. 3 illustrates an example system 300 for testing a
nanofluidic device 200. For example, the system 300 can image a
reaction between the calcite channels 207 and a fluid. The
nanofluidic device 200 is positioned on a sample stage 324 located
inside a chamber 322. The chamber 322 can isolate the device 200
from outside interference and can be evacuated--that is, a vacuum
can be produced within the chamber. Fluid, such as brine solution,
can be introduced to the device by inlet line 203, and the fluid
can exit by outlet line 205. As fluid flows into and out of the
device 200, an electron beam gun 320 emits an electron beam to
produce an image of the calcite channels 207 while interacting with
the fluid. The electron beam gun 320, chamber 322, and sample stage
324 can be components of a single apparatus, such as an SEM. In
certain implementations, the electron beam gun 320 is the same
source of electrons used to perform electron beam lithography in
fabricating the nanofluidic device 200, for example, a modified SEM
capable of performing electron beam lithography.
[0022] Calcite reservoirs are typically heterogeneous. Some areas
of the reservoir can contain large voids, whereas other areas can
have poor connectivity and low permeability. Acid injection is an
enhanced oil recovery method that can increase the connectivity of
an area of a reservoir. Acid injection can include a brine solution
213 with acid content, for example 10% hydrochloric acid. Acid
injection causes carbonate dissolution, and the dynamics of
formation dissolution due to acid flow on a pore-scale and an
atomic-scale can determine the net flow behavior. The dynamics can
also determine other reservoir characteristics such as likelihood
for leakage, oil and gas recovery, and storage capacity. As brine
solution 213 flows through the nanofluidic device 200, the SEM can
be utilized to observe calcite dissolution and preferential flow of
brine at a nanometer scale in the device 200. The observations can
then be used to quantify acid dissolution of carbonates and to
predict the migration of brine through aquifers, such as calcite
formations.
[0023] FIG. 4 is a flowchart illustrating an example method 400 for
fabricating a calcite channel nanofluidic device. At 402, a silicon
substrate is prepared to be the bottom of the nanofluidic device.
The size and shape of the substrate can be determined by a sample
stage 324 of an SEM. In certain implementations, the nanofluidic
device is packaged, and the size of the substrate is smaller than
the sample stage 324. Substrate preparation can include cleaning of
the substrate. At 404, photoresist is coated on the substrate, for
example, by spin coating. A number of parameters can determine the
thickness of the coated layer of photoresist such as a spin rate,
photoresist viscosity, temperature, and other parameters. In some
implementations, the thickness can equal a desired height of
calcite channels in a nanofluidic device. In certain
implementations, the photoresist is a negative photoresist, such as
PDMS or SU-8. At 406, channel patterns are formed using electron
beam lithography. Forming channel patterns involves exposing a
portion of the photoresist to a beam of electrons, for example,
from an SEM. At 408, the exposed portion of the photoresist is
developed, that is, removed. Developing the photoresist involves
dissolving the photoresist using a solvent, such as PGMEA, ethyl
lactate, or di-acetone alcohol. Developing the photoresists also
involves revealing a portion of surface of the substrate. At 410,
calcite is deposited in the channel patterns using atomic layer
deposition with calcite precursor gas. Atomic layer deposition
involves depositing calcite, layer by layer. In certain
implementations, calcite is deposited layer by layer until the
calcite channel height is similar to or the same as the original
height of the coated photoresist at 404. At 412, the remaining
portion of photoresist is dissolved using a solvent. The calcite
channel structure deposited on the substrate and the substrate
remain. The formed calcite channels can have a length in a range of
50 to 100 nm in at least one dimension. At 414, the device, which
includes the substrate and calcite channels, is packaged in a
casing. The casing can include a top portion with a window, a
bottom portion that can hold the device, an inlet connection to
allow a fluid to enter the device, and an outlet connection to
allow the fluid to exit the device. The window can be made of an
electrically conductive and optically transparent material, such as
SiN, and can be set on top of the calcite channels deposited on the
substrate. In certain implementations, the package includes a metal
casing around the substrate.
[0024] While this specification contains many specific
implementation details, these should not be construed as
limitations on the scope of any invention or on the scope of what
may be claimed, but rather as descriptions of features that may be
specific to particular implementations of particular inventions.
Certain features that are described in this specification in the
context of separate implementations can also be implemented, in
combination, in a single implementation. Conversely, various
features that are described in the context of a single
implementation can also be implemented in multiple implementations,
separately, or in any suitable sub-combination. Moreover, although
previously described features may be described as acting in certain
combinations and even initially claimed as such, one or more
features from a claimed combination can, in some cases, be excised
from the combination, and the claimed combination may be directed
to a sub-combination or variation of a sub-combination.
[0025] Particular implementations of the subject matter have been
described. Other implementations, alterations, and permutations of
the described implementations are within the scope of the following
claims as will be apparent to those skilled in the art. While
operations are depicted in the drawings or claims in a particular
order, this should not be understood as requiring that such
operations be performed in the particular order shown or in
sequential order, or that all illustrated operations be performed
(some operations may be considered optional), to achieve desirable
results.
[0026] Moreover, the separation or integration of various system
modules and components in the previously described implementations
should not be understood as requiring such separation or
integration in all implementations, and it should be understood
that the described program components and systems can generally be
integrated together in a single software product or packaged into
multiple software products.
[0027] Accordingly, the previously described example
implementations do not define or constrain this disclosure. Other
changes, substitutions, and alterations are also possible without
departing from the spirit and scope of this disclosure.
* * * * *